In some vehicles, vacuum is used to operate or assist in the operation of various devices. For example, vacuum may be used to assist a driver applying vehicle brakes, turbocharger operation, fuel vapor purging, heating and ventilation system actuation, and driveline component actuation. If the vehicle does not produce vacuum naturally, such as from the intake manifold, then a separate vacuum source is required to operate such devices. For example, in some boosted engines where intake manifold pressures are often at pressures greater than atmospheric pressure, intake manifold vacuum may be replaced or augmented with vacuum from an evacuator.
As used herein, an evacuator is defined as a converging, diverging nozzle assembly with three connections, a motive port, a discharge port, and a suction port connected to a device requiring vacuum. The evacuator may be an ejector or an aspirator, depending on the pressures at the motive and discharge ports. Specifically, if the pressure at the motive port of the evacuator is at atmospheric pressure and if the discharge port is less than atmospheric pressure, then the evacuator may operate as an aspirator. If the pressure at the motive port of the evacuator is greater than atmospheric pressure and the discharge port of the evacuator is less than the pressure at the motive port but at least atmospheric pressure, then the evacuator operates as an ejector. A low pressure region may be created within the evacuator so that air can be drawn from a vacuum reservoir or may directly act on a device requiring vacuum, thereby reducing pressure within the vacuum reservoir or device requiring vacuum.
Those skilled in the art readily understand that the various vacuum consuming devices in a vehicle typically include different requirements for suction vacuum as well as suction flow rate. For example, a fuel vapor purge canister produces a continuous flow requiring a low level of vacuum, over a longer period of time when compared to a brake boost canister. However, the brake boost canister typically requires relatively higher suction vacuum when compared to the fuel vapor purge canister. Moreover, a crankcase ventilation system needs to be purged continuously, and therefore requires a constant supply of vacuum. In contrast, the fuel vapor purge canister may only need purging for a specified period of time after starting of the vehicle.
Some existing vehicles may supply vacuum to each of the devices requiring vacuum (i.e., the brake boost canister, fuel vapor purge canister, etc.) separately. This current approach for providing vacuum results in an increased number of parts, complexity, and cost to the vehicle. Thus, there is a continuing need in the art for an improved, low-cost approach for providing both high suction vacuum and high suction flow rate to multiple vacuum consuming devices within a vehicle.